The 16 best Eurorack modules: our guide to finding the right module to build, or expand your modular synthesizer system

VCOs, VCAs, filters, LFOs, sequencers and more...

The booming world of Eurorack can be difficult to negotiate, with new manufacturers popping up all the time, and many versions of the same basic module types.

Such a minefield can leave you bemused and wondering; which envelope to choose? Digital, or analogue oscillators? What type of filter? How many sequencers do I need?

This guide aims to provide a run down of the best module in each category to help you put together or expand your system. Featuring modules both old and new, the focus here is on flexibility: modules that can fulfil several roles in a system or that really cover all the bases of a given module type.

Crucially however this shouldn't be at the expense of ergonomics and playability. Hardware is all about getting hands on with your equipment and having fun with your music.

1. Mutable Instruments Plaits

Aux output can be used for a stereo signal with many of the model types

Dedicated CV input for model selection

Aux output is often a lower signal level than the main out

With their successor to the mighty Braids, Mutable Instruments has re-designed both hardware and software, simplifying the interface to make Plaits more streamlined and playable. The eight synthesis models for pitched sounds offer plenty of variety: all killer no filler! A digitally modelled low-pass gate can be used to shape not just the audio output but also internal modulation of two timbre controls and FM giving you a full synth voice in only 12HP. The other eight models for noise and percussion make this a versatile sound source that will always have a place as your system grows.

The Rubicon2 from Intellijel builds on it's predecessors prowess to offer probably the most versatile analogue oscillator currently on the market. With nine separate waveform outputs, tuning via an 8-octave switch, hard or flip sync options, wave-folding via the unique Warp circuit and a limiter in case the signal gets too hot. Crucially the thru-zero FM now features a lock switch providing pitch compensation, meaning no change in pitch or tracking accuracy even with the fiercest modulation. This is an analogue oscillator that can really compete with the flexibility of digital.

3. Instruo Cš-L

Three types of audio modulation which can also be used with external signals

Sub-oscillator with octave switch

Dual final outputs each with their own wave folder

Panel layout can make some controls tricky to get to

The Cš-L from Instruo builds on the classic Complex Dual Oscillator concept that has its origin in the 261e Buchla module of the '70s and recent iterations like the Make Noise DPO. What sets the Cš-L apart is the internal routing and modulation bus which presents a host of synthesis options before you even plug in a cable. The bottom oscillator is a Triangle core, the top oscillator a more aggressive Saw core that can also run at LFO speeds. Unlike most Complex Oscillators either can act as Modulator or Primary. Once you start self patching the range of tones you can tease out of this module is huge.

Joranalogue proclaim the Filter 8 as the 'cutting edge in modular VCF design'. Based on the 'classic' OTA 4 pole cascaded low pass topology it emerges with a sound all its own. The Filter8 features four separate low pass outputs with differing filter slopes plus high pass, bandpass & notch, phase shift, and standard bandpass for a real variety of filter flavours. Filter8's unique resonant feedback circuit enables you to push the resonance hard without the loss of bass frequencies. Furthermore when set to self-oscillate the module will function as an eight phase sine wave VCO with tracking over 5 octaves, and in low frequency mode as an eight output slew modifier or an eight phase LFO.

MI's Stages is an extremely flexible six stage envelope generator, with CV control over each section. What's more those six stages can be broken down into six separate release envelopes, or anything in between. Going even further each stage can loop to create six sync-able LFOs or even a six step pitch sequencer. A looping stage can also be used as a clock multiplier/divider or a square wave sub-oscillator for your VCO. Extremely versatile yet straight forward in operation, there's always going to be a use for this module in your patch.

The saying in Eurorack is that you can never have enough VCAs. With Intellijel's Quad you get four fully featured VCAs in one module, giving you plenty of potential beyond simply shaping the final output level of your patch. Each VCA has adjustable level control and a mix knob for linear/exponential response. Both the CV inputs and the VCA outputs are cascaded, enabling you to use adjacent sets for sub mixes or the whole module as a four channel mixer. There is also a boost switch to amplify weak signals by +6db, and the inputs distort nicely when pushed hard if you want to add a bit of bite to your sound.

The Batumi from XAOC is a fully featured quad LFO in only 10hp. Combining power & flexibility in a small package this has become the must have LFO in most racks. Each channel features 3 different wave outputs with the expander giving the option to switch the Saw output to three other variants. The LFOs can be used independently or in three modes where they are inter-related (quadrature/phase/ divide). They can be free running or synced/reset with a clock input. The optional 'expert' firmware increases the flexibility at the expense of the straight forward operation of the normal mode.

Marbles combines the concept of the Turing Machine and MI's own Grids and Branches to provide a plethora of random outputs which can be locked into repeating patterns, with a master tempo that can be varied from rigid metronome to wild off kilter rhythm. One side of the module focuses on gates, the other side on smooth or stepped voltages which can be free or quantised in a variety of ways. The centre output provides a constantly fluctuating random voltage which is perfect for patching back into the module. While Marbles can fulfil all the standard random voltage needs it really excels as a source of musical and rhythmic inspiration.

Intellijel's Metropolis has been around for years but for my money it's still the best Eurorack sequencer, largely due to its hands on playability. eight sliders set your pitch, steps can be toggled on and off and a fantastic acidic pitch bend funks things up. The latest firmware adds ratcheting per step and the ability to save eight different sequences for instant recall. Two assignable CV inputs can be used for adjusting parameters such as gate length and pitch or key transposition. The Metropolis is straightforward enough to pick up and jam with straight away but there's depth to explore that will keep you coming back.

Erica Synths Drum Sequencer claims to be the final solution for your rhythm sequencing needs. Aimed squarely at the house and techno producer with a classic 909-style button interface. At 42HP it's a very big module, it's plain to see Erica Synths has opted for playability over portability here. But it offers a lot of features: with 16 outputs and 14 accents for drums. A separate CV and Gate for a Bass Synth, Swing, Probability, Mute/Solo and Pattern linking, it covers all the bases of a modern drum sequencer with style.

The Blackhole 2 DSP is an updated version of Erica Synths superb stereo multi FX module, based on the same Spin FV1 chip as Tiptop's Z-DSP. The 24 custom effects (8 more than the original are mostly Reverbs and Delays with Chorus/Flanger/Phaser and a few others thrown in. The sound is full of character and probably best described as having a 90's vibe. To dial in even more grittiness the Crush control directly reduces the bit-rate of the processor chip. All settings can now be saved with each patch for ease of switching in a live situation.

Maths from Make Noise is often described as a Swiss Army knife for Eurorack. At its most basic it's a pair of very snappy AD voltage controlled envelopes or a pair of LFOs that'll run as slow as 26 minutes a cycle! But Maths is called a function generator for a reason, the number of different roles it can fill is huge, and as a gateway to grasping the depth of modular synthesis it can't be beaten. Get one, and learn how to really use it.

Strymon's first Eurorack module Magneto is a superb four head stereo tape delay emulation. A well designed interface makes it great fun to play, while a host of CV inputs offer plenty depth and scope for experimentation. Delays can range from crisp and clear to warm over-driven and warbly. The fantastic built in spring reverb emulation adds space and the pitch-shifted delay option means you can also use the module as a chord or sub bass generator. If you drive the feedback into self oscillation you can even use the Magneto as a wild oscillator.

Ritual Electronics first module Miasma is a voltage controlled Distortion. The large and very wiggle friendly Feedback knob lets you know what this module is all about. With the feedback turned up you can easily push the module into self-oscillation even without an input signal. This feedback path can be opened and the signal fed through other effect modules hugely expanding the sound design possibilities. The tone of Miasma is also modifiable at the hardware level. The two rectification diodes (one for each polarity of the signal) are accessible at the back of the module and it comes with a variety of extras so you can swap them around to vary the tone from warm fuzz to Industrial distortion. An expander will be available shortly so you can change diodes with a switch.

The new version of Pam's Workout from ALM takes the concept of Clock modulation and expands it in all kinds of sync-able loop-able directions. It's core clock is rock solid and it'll connect to all your different studio gear so it's perfect as a master clock. Each of it's 8 outputs can be humanised, phase shifted, delayed and swung. Euclidean or probability based step skipping can be used for rhythm creation. The wave output can also be altered to give you a whole host of synced LFOs. Pam's New Workout offers a huge array of modulation possibility in a small package. It's power is enough to justify it a place here as the only module in the list with a screen and menu system.

The One from Tiptop Audio offers extremely low latency sample playback from a micro SD card, making it ideal for drum and percussion samples. For pitch based material it features a built in quantizer option with a range of scales. The CV input can also be used to switch between different samples on the fly to broaden your sound palette. Unfortunately this will increase the latency so it's not really suitable for drum samples. The module is also DC coupled so you can also use it to output control voltage: playing back samples of LFOs, envelopes or random voltages. The One comes with 60 sounds included, with other sample cards available from Tiptop, or you can make your own of course.